Rank lost after a win?

[Atorrante]

Welcome to the wonderful world of OGS.
Maybe this topic will help you in understanding the ranking system.

"The" explanation of why your rank can go down after winning a game

I wish I was about to type a great explanation of why your rank can go down after you win one game. But I don’t clearly understand it - I have an inkling, but not a firm grasp. Can someone explain it in a straightforwards way?